@rose I was wondering if Peter actually only meant Rishda or could he refer to anyone as Tash's lawful prey. I think CS Lewis could have been more clear on this.

I think it may have been because Rishda have been using Tash's name randomly, though not believing in him (secretly, he's an atheist). He had been playing with fire. He called on Tash unintentionally.

I think Rishda would be like the religious leaders of Jesus's days. The religious leaders were following the religious rules, saying they were doing things for God, yet they never realized they were actually doing things for the devil. They never realized they belonged to Satan.

Rishda was doing all things in the name of Aslan, working for Shift (though eventually he got tired of Shift doing everything). He blended the two names, Aslan and Tash, "Tashlan" (I'm sure he did that to impress both the Narnians and Calormenes). Then when he realized that Tash was real, he tried to make up for it by hurling all of Tirian and his army into the stable, and set the stable on fire to make an offering to Tash. Though he does get thrown into the stable himself. So I guess you could say he got a taste of his medicine for his cruelty.

So I think CS Lewis could have been more clear on how what made Rishda Tash's lawful prey. And could Peter have refereed to anyone as Tash's lawful prey.

My best guess is that Rishda and Shift were saying Tash wanted things that Tash didn't want (like the squirrels donating their food, etc) and Tash was offended by that. But that kind of makes Tash sound good or at least reasonable, and you really get the vibe Tash is evil, so that's questionable. 

Rishda employed treachery, and therefore is culpable under the Emperor-Over-the-Sea's laws?

Just a quick off-the-cuff take on it.

There is a famous quote from the Poet John Ruskin where he uses the phrase "lawful prey".

In simple terms, he uses it as a means to suggest that in financial transactions, people who expect to get "something for nothing", usually deserve to be duped (the quote itself, linked below, is at little bit more complex than that, but its the same point)

https://www.lifeofanarchitect.com/john-ruskin-common-law-of-business-balance/

Essentially he uses the term "Lawful Prey" in the same usage as the phrase "Fair Game" to indicate that something is rightfully up for grabs or able to be exploited due to circumstance ("Game" in this context meaning an animal hunted for sport)

In the context of Narnia, I think that in both these instances (WW & Tash), CS Lewis has used the phrase "lawful prey" in a somewhat similar way - not as any allusion to an actual written set of laws, but rather to indicate that bad things exist in Narnia for a reason. They don't exist out of accident, or through negligence on Aslan's part, but rather they form an element of natural Justice - that people who do wrong, get what they deserve.

You know it's funny - and I don't know if anyone has mentioned this before - but I just saw the episode of "Into the Wardrobe" theorizing about the origins of Tash, and... well to be honest his last one kind of bothered me.  In case you haven't seen it, the idea he had was that Tash was a demonic creature from Charn, and that the "terrible price" Jadis payed to learn the Deplorable Word was essentially selling her soul to Tash.  In other words, she was basically possessed by Tash through the entire series.

On the one hand, it would (as he said) explain a lot of things; he lists a few in the video, like her "maniacal behavior" in MN and her super-human strength.  But she wasn't human - on top of being 7 feet tall she was half-giantess, so the strength is easily explained by that IMO.  And as for her behavior, she was trying to conquer our world - of course she wouldn't be all quiet and refined like an established queen.  He also says it explains the "lawful prey" thing, and I can kind of see that.  For one, from an allegorical standpoint, it would make a lot of sense.  In our world, Satan will be around until our Last Battle; But Narnia's original (and IMO worst) evil... was killed off in the first book?  It always struck me as odd.  But if it was Tash behind the scenes the whole time, well now we have Aslan dealing with Narnia's "devil" once and for all at the end of time, which is a much closer parallel to our world.  There's also the picture of a creature like Tash in that illustration, as he pointed out, so it's not a totally groundless theory.

But here's why this theory kind of drives me nuts:  For one it kind of makes Jadis an almost sympathetic character - she was just a puppet.  It means she might have seen her final independent action, giving herself to Tash, as a noble sacrifice.  Now granted this could be some bias on my part, because I found her so terrifying as a kid (and the thought of her just being a pawn is laughable at best, a monster-of-a-character who literally appeared in nightmares being not near as bad as she seemed).  But it doesn't stop there: there are some serious holes in this theory that I just don't see how it could work.

• First of all, at the end of MN she fled north - not south.  And then she wouldn't come within a hundred miles of the fruit.  The only way I could see her even getting to Calormen without going through Narnia (or the western woods, which also have that tree - the one Digory picked an apple from) would be to sail there.  And we're talking the whole Bight of Calormen, literally across the world.  And for what?  To establish her/himself as a deity and then leave?
• Which brings me to the second point: if Tash were controlling Jadis, and set himself up as a god, and wanted to conquer Narnia, don't you think he'd have stayed down with the people who worshiped him, mounting an army and then attacking from the south like Rabadash like in HHB?  I mean it could have happened like that in the years between MN and LWW, so I guess it might have been possible, but it just doesn't make sense why he would stay up north with the giants - he had a whole kingdom ready to follow him against Aslan.
• In Charn, Jadis is obviously speaking from her own perspective.  She says things like "my sister", and "I was the Queen", and "**I** paid a terrible price to learn it".  If she were just the vessel of Tash, what would be the point of all that third- (fourth?) person exposition (lol)?  Even if Tash had access to her memories, what would be the advantage of pretending to be Jadis?  I think she was who she said she was, and Tash was something else entirely.
• It's also possible that the whole "lawful prey" thing was simply that with Jadis gone, the right to kill under the Deep Magic now belonged to Tash.   Or as someone else said, maybe it was just meant like "fair game".

Anyway, the one conclusion I did agree with is that we'll never know for sure.  That's something I love about Narnia - there are stories we know and love, but there are countless untold stories that leave room for random conversations like this. 🙂  But when I saw that video, I was like, hang on, seriously?  I gotta think about this one.  That would be so messed up!  Oh yeah, then why this and that and nope, can't be.  😀  But all joking aside, if you've read this far down into my post/rant, then thanks for putting up with me tonight (lol).

@geekicheep thanks for taking that one out and trouncing it! I don't like Narnia being reinterpreted in terms of 21st century superhero and arch-villain stories!

I too have a dislike for weird theories and interpretations that get popularised by having books published about them.
People who do such things often haven't read Lewis's non-fiction works, especially the ones explaining his faith.

What made Rishda Tash's lawful prey, C.S Lewis never says. It is left for our own interpretation.

As I've mentioned in the Narnia in the Bible thread, I don't think Rishda was Tash's lawful prey because he was a rich and powerful man. It may have been abuse of power. It may have been that he was doing all things in the name of Tash, though not believing in him. His power and wealth may have got in the way of his worship of Tash and neglected the poor and needy. You can almost think of him as the rich man in the story Jesus told about a rich man and a beggar. The rich man neglected the beggar, and we would not give him scraps that fell from his table. Also, possibly, his wealth got in the way of his worship of God. 

Another might be how did Tash know Rishda's name? There's no indication that Rishda had a name tag on that said, "Hey everyone, I'm Rishda Tarkaan." You might recall that Aslan said that Jadis's knowledge only goes back to the Dawn of Time. It's possible that Tash has limited knowledge as well. He probably was intelligent, but his knowledge may have been limited.